Recently, the downsizing and performance improvement of the electronic devices are under rapid development. Also, the improvement of the transmission speed and the lowering of driving voltage in a circuit component in use progress remarkably as seen in the high-speed transmission systems such as the antenna circuit in the cell phone, the RF module, USB 2.0, and USB 3.0, S-ATA2, HDMI (Registered Trademark) or the like. On the contrary, with the downsizing of the electronic device or the lowering of driving voltage of the circuit component, the breakdown voltage of the electronic components which are used in the electronic devices decreases. In this respect, to protect the electronic components from overvoltage becomes an important technical subject, for example, to protect the electronic components against the electrostatic pulses generated when the human body is brought into contact with the terminals of an electronic device.
In the past, in order to protect the electronic components from such electrostatic pulses, a method of providing a laminated varistor between the ground and a line to be subjected to static electricity has generally been used. However, the laminated varistor usually has a relatively high electrostatic capacity which is the main cause for the deteriorated signal quality when the laminated varistor is used in the high-speed transmission system. In addition, an ESD protection device having a large electrostatic capacity cannot be used in an antenna circuit or an RF module. In this respect, an ESD protection device with a small electrostatic capacity is required to be developed which is applicable to the high-speed transmission system.
An ESD protection device has been suggested as the ESD protection device having a low electrostatic capacity which has two separately and oppositely disposed electrodes between which two a composite of a conductive inorganic material and an insulating inorganic material is arranged as a discharge inducing section. Similar to the laminated varistor, such an ESD protection device is disposed between the ground and a line to be subjected to static electricity. If a much too high voltage is applied, discharge will occur between the electrodes of the ESD protection device and then the static electricity will be introduced into the ground side.
Such an ESD protection device provided with the gap typed electrodes possesses characteristics such as a high insulation resistance, a small electrostatic capacity and a good responsiveness. In another respect, a problem rises that the electrodes and the conductive inorganic material inside the discharge inducing section will agglutinate due to the heat or stress generated during the discharge process to cause a short-circuiting.
The technique disclosed in, for example, Patent Document 1 has been proposed as one for inhibiting the short-circuiting caused by the discharge. Patent Document 1 has disclosed an ESD protection device characterized in that the oxides of the metal such as aluminium or magnesium are attached to the surface of discharge electrode in a gap typed discharge element containing a pair of discharge electrodes oppositely disposed in a hollow space. With such a configuration, as the oxide attached to the discharge electrode is the oxide with a high insulation resistance, the short-circuiting between the oppositely disposed electrodes can be prevented from happening and the durability against the repeatedly applied static electricity can be improved.